Basic and ultrabasic coastal dykes adjacent to the São Sebastião Channel, north coast of the state of São Paulo

Abstract

The portions of the Precambrian Costeiro Complex adjacent to the São Sebastião Channel (São Paulo State, Brazil) are crosscut by mafic dykes of basic to intermediate composition, lamprophyres and trachytes. The former have been correlated with the basalts of the Paraná Basin, while the lamprophyres are expressions of an alkaline magmatism different from the one that happened approximately 80 Ma ago in the São Sebastião, Búzios, Vitória and Montão de Trigo islands, where more acid terms predominate with associated trachytes and rare phonolites. The basic-ultrabasic lamprophyric magmatism is widespread along the São Paulo and Rio de Janeiro coasts; they are independent from and most likely older than the stocks and alkaline massifs.